Hancock describes himself as an "unconventional thinker who raises controversial questions about humanity’s past".[5] Prior to 1990 his works dealt mainly with problems of economic and social development. Since 1990 his works have focused mainly on speculative connections he makes between various archaeological, historical, and cross-cultural phenomena.

Canadian author Heather Pringle has placed Graham Hancock within a particular pseudo-intellectual tradition going back at least to Heinrich Himmler's infamous research institute, the Ahnenerbe. She specifically links Hancock's book Fingerprints of the Gods to the work of Nazi archaeologist Edmund Kiss, a man described by mainstream scientists of the time as a 'complete idiot'.[8]

In Hancock's book Talisman: Sacred Cities, Secret Faith,[9] co-authored with Robert Bauval, the two put forward "a version of the old Jewish-Masonic plot so beloved by ultra-right-wing conspiracy theorists."[10] They suggest a connection between the pillars of Solomon's Temple and the Twin Towers, and between the Star of David and The Pentagon.[11] A contemporary review of Talisman by David V. Barrett for The Independent pointed to a lack of originality as well as basic factual errors, concluding that it was "a mish-mash of badly-connected, half-argued theories".[12] In a 2008 piece for The Telegraph referencing Talisman, Damian Thompson described Hancock and Bauval as fantasists.[13]

Hancock's Supernatural: Meetings With the Ancient Teachers of Mankind, was published in the UK in October 2005 and in the US in 2006. In it, Hancock examines paleolithiccave art in the light of David Lewis-Williams' neuropsychological model, exploring its relation to the development of the fully modern human mind.

In 2015, his Magicians of the Gods: The Forgotten Wisdom of Earth’s Lost Civilization was published by St. Martin's Press.

His first novel, Entangled: The Eater of Souls, the first in a fantasy series, was published in the UK in April 2010 and in the US in October 2010. The novel makes use of Hancock's prior research interests and as he has noted, "What was there to lose, I asked myself, when my critics already described my factual books as fiction?"

His books have sold more than five million copies worldwide and have been translated to 27 languages.[citation needed]

Representation of the central tenet of the OCT – the outline of the Giza pyramids superimposed over a photograph of the stars in Orion's Belt. To achieve this concordance the pyramids have been rotated and scaled to suit. The validity of this match has been called into question by Hancock's critics, as noted in the text.

One of the many recurring themes in several of Hancock's works has been an exposition on the "Orion correlation theory" (or OCT),[14][15] first put forward by Belgian writer Robert Bauval and then further expounded in collaborative works with Hancock, as well as in their separate publications.

BBC Two's Horizon TV series broadcast a programme, Atlantis Reborn, on 4 November 1999 that challenged the ideas presented by Hancock. It detailed one of Hancock's claims that the arrangement of an ancient temple complex was designed to mirror astronomical features and attempted to demonstrate that the same thing could be done with perhaps equal justification using famous landmarks in New York. It also alleged that Hancock had selectively moved or ignored the locations of some of the temples to fit his own theories (see below).[16]

Hancock claimed he was misrepresented by the programme, and he and Robert Bauval made complaints to the Broadcasting Standards Commission against the way Horizon had portrayed them and their work. Eight points were raised by Hancock, two by Bauval (one of which duplicated a complaint of Hancock's).[17] These included the complaint that:

The programme had created the impression that he [Hancock] was an intellectual fraudster who had put forward half baked theories and ideas in bad faith, and that he was incompetent to defend his own arguments. Adjudication: [The Commission] finds no unfairness to Mr Hancock in these matters.[18]

The BSC dismissed all but one of the complaints. Overall, the BSC concluded that "the programme makers acted in good faith in their examination of the theories of Mr Hancock and Mr Bauval".[19] The complaint which was upheld was that

The programme unfairly omitted one of their arguments in rebuttal of a speaker who criticised the theory of a significant correlation between the Giza pyramids and the belt stars of the constellation Orion (the "correlation theory")

which the Commission did find to be unfair. That speaker was the astronomer Edwin Krupp. Krupp argued that Bauval had fudged the maps of Orion and the Pyramids by placing them upside down in terms of stellar directionality to make the theory work.[20] The BBC was not obligated to do more than broadcast an apology for the single point of unfairness but made a decision to modify the Orion sequence to demonstrate that the overall argument of the film remained intact.

In Atlantis Reborn Again, shown on 14 December 2000, Hancock and Bauval provided further rebuttals to Krupp and argued that the ancient Egyptians had made the Pyramids correlate with the three stars of Orion's Belt. However, the documentary as a whole continued to present serious doubts about Hancock's claims, demonstrating as an example how, by using his methods, the constellation of Leo may be 'discovered' among landmarks of modern Manhattan, concluding: 'As long as you have enough points and you don't need to make every point fit, you can find virtually any pattern you want.'[21]

Hancock gave a TEDx lecture titled “The War on Consciousness”, in which he outlined a case for the use of ayahuasca, an amazonian tea containing an hallucinogenic and illegal compound DMT. While making clear that drinking ayahuasca may often be a physical ordeal, and that he did not approve of its use for casual recreation, he said that it may be essential for self-improvement, spiritual growth and social progress, as well as for curing drug addiction. He revealed that until relatively recently he had maintained a 24-year-long daily cannabis habit during which he was “stoned for 16 hours a day”, and had suffered from rages and paranoia as a result. Hancock said he had been successfully cured by an experience with ayahuasca in South America, during which he experienced an arduous life-review by the Amerind spirit “Mother Ayahuasca”.[22]

The lecture was removed from the TEDx YouTube channel by the TED organisers after the recommendation of TED's Science Board.[23]

In 2009, Roland Emmerich released his blockbuster disaster movie 2012, citing Fingerprints of the Gods in the credits as an inspiration for the film,[24] stating: "I always wanted to do a biblical flood movie, but I never felt I had the hook. I first read about the Earth's Crust Displacement Theory in Graham Hancock's Fingerprints of the Gods."[25] Also in 2009, author Geoff Stray released his best-selling book Beyond 2012: Catastrophe or Awakening? in which he cites Graham Hancock as one of his inspirations and as a guidepost to point others to do their own investigation into the wonder of ancient societies.[26]

^"...the belief of Hancock and other writers in a lost civilisation that passed its wisdom on to ancient Egypt or the Maya repeats the theme of Atlantis: the antediluvian world popularised by Ignatius Donnelly from 1882." Kevin Greene, Tom Moore, Archaeology: An Introduction, page 252 (Routledge, 2010 edition). ISBN 978-0-203-83597-5